Table of contents
The bearings:
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Combined needle roller bearing / needle roller bearing: Fr = radial load Fa = axial load
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Design variants
The standard product range of combined needle roller bearings comprises:
The majority of these needle roller bearings are X-life bearings ➤ link.
The bearings comprise a radial component and an axial component
Combined needle roller bearings comprise a radial needle roller bearing, which is combined with an axial bearing component ➤ Figure, ➤ Figure and ➤ Figure. These bearings can support radial as well as axial loads with just one bearing and permit locating bearing arrangements with only a small radial design envelope ➤ Figure and ➤ section. They are suitable, for example, where radial and axial loads are present and simple axial contact washers are no longer able to support the axial loads on account of their size, high speeds or inadequate lubrication, and other locating bearings require too much installation space.
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Combined needle roller bearings, radial and axial dynamic load carrying capacity Cr = radial basic dynamic load rating Ca = basic axial dynamic load dating |
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Suitable for compact direct bearing arrangements on the shaft
Needle roller/axial deep groove ball bearings do not have an inner ring and are therefore particularly compact in a radial direction ➤ Figure. However, they require a shaft raceway that is hardened and ground ➤ section. If the shaft cannot be used as a rolling bearing raceway, inner rings IR can be used instead ➤ Figure. The suitable inner rings are given in the product tables and must be ordered in addition to the bearing ➤ link. For lubrication, the outer ring of the radial bearing component has a lubrication groove and lubrication holes.
The rolling element set for the axial bearing component is a full complement ball system
Needle roller/axial deep groove ball bearings NX and NX..-Z have a full complement ball set and an extremely low radial section height ➤ Figure. Due to the compact radial dimensions, bearing arrangements can be achieved with very small shaft centre distances, such as those that may be present in multi-spindle drilling machines. A sheet steel end cap secured to the radial bearing component grips the shaft locating washing of the axial bearing and holds the axial bearing component together ➤ Figure. As a result, the bearings are self-retaining. The sheet metal caps for bearings NX have lubrication holes for oil lubrication ➤ Figure and ➤ section.
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Needle roller/ axial deep groove ball bearing NX without inner ring Fr = radial load Fa = axial load
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Needle roller/axial deep groove ball bearing NX..-Z with inner ring
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The rolling element set for the axial bearing component is guided by a cage
In bearings NKX and NKX..-Z, the rolling element set is not a full complement ball system, as is present in bearings NX, but is retained by a cage ➤ Figure. The ball and cage assembly corresponds to an axial deep groove ball bearing of series 511. As a result of the cage, these bearings are suitable for higher speeds than bearings of the full complement design ➤ link.
Type NKX
Bearings NKX are not self-retaining, i. e radial needle roller bearing, axial ball and cage assembly and shaft locating washer can be fitted independently of each other ➤ Figure.
Type NKX..-Z
Type NKX..-Z has a sheet steel end cap, which holds the axial bearing component together, i. e. the bearings are self-retaining. The cap is designed without lubrication holes and is rigidly connected to the housing locating washer of the radial bearing component ➤ Figure.
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Needle roller/axial deep groove ball bearings without inner ring Fr = radial load Fa = axial load
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The rolling element set for the axial bearing component is guided by a cage
These bearings comprise a radial needle roller bearing and an axial cylindrical roller bearing of series 811 with a plastic cage. They do not have an inner ring and require a shaft raceway that is hardened and ground ➤ Figure and ➤ section. If the shaft cannot be used as a rolling bearing raceway, inner rings IR can be used instead ➤ Figure. The suitable inner rings are given in the product tables and must be ordered in addition to the bearing ➤ link. For lubrication, the outer ring of the radial bearing component has a lubrication groove and lubrication holes.
Type NKXR
Type NKXR is not self-retaining, i. e. the radial needle roller bearing, axial cylindrical roller bearing and shaft locating washer can be fitted independently of each other ➤ Figure.
Type NKXR..-Z
A sheet steel end cap secured to the radial bearing component grips the shaft locating washing of the axial cylindrical roller bearing and holds the axial bearing component together. As a result, these bearings are self‑retaining ➤ Figure.
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Needle roller/axial cylindrical roller bearings without inner ring Fr = radial load Fa = axial load
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Needle roller/axial cylindrical roller bearing NKXRwith inner ring
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The rolling element set for the axial bearing component is guided by a cage
Needle roller/angular contact ball bearings comprise a radial needle roller bearing, an angular contact ball bearing as the axial component and an inner ring ➤ Figure and ➤ Figure. In the case of type NKIA the inner ring is of a single-piece design, whereas design NKIB has one narrow and one wide inner ring. The ball cage of the axial bearing component is made from plastic ➤ Figure and ➤ Figure and ➤ section. The bearings have a low radial section height and are suitable for high speeds ➤ link. As needle roller/angular contact ball bearings are not self-retaining, the inner ring can be mounted independently of the outer ring and needle roller and ball set. During fitting it must, however, be ensured that the bearing rings are not interchanged with rings from other bearings, but are always mounted in the delivered matched pair.
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Needle roller/angular contact ball bearing NKIA Fr = radial load Fa = axial load |
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Needle roller/angular contact ball bearing NKIB Fr = radial load Fa = axial load
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The combined needle roller bearings described here are X-life bearings. They are characterised by a very high load carrying capacity and long rating life. This is achieved, for example, through the modified internal construction and optimised contact geometry between the rolling elements and raceways, as well as through the higher quality of the steel and rolling elements, higher surface quality and appropriate heat treatment.
Increased customer benefits due to X-life
The technical enhancements offer a range of advantages, such as:
Lower operating costs, higher machine availability
In conclusion, these advantages improve the overall cost-efficiency of the bearing position significantly and thus bring about a sustainable increase in the efficiency of the machine and equipment.
Suffix XL
Combined needle roller bearings in X-life quality include the suffix XL in the designation ➤ Figure to ➤ Figure and ➤ link.
X-life indicates a high product performance density and thus a particularly significant benefit to the customer.
Suitable for moderate axial loads
Needle roller/axial deep groove ball bearings support high radial loads and moderate axial loads in one direction ➤ Figure to ➤ Figure. Bearings with a full complement ball set have a higher axial load carrying capacity than bearings with a cage-guided axial component ➤ Figure.
Mounting of two needle roller/axial deep groove ball bearings in a mirror image arrangement
Needle roller/axial deep groove ball bearings can support axial loads in one direction only. If no temperature-induced changes in length occur during operation in an arrangement of short shafts, two bearings can also be used to support axial loads in both directions, which are then mounted in a mirror image arrangement ➤ Figure. The bearing parts should, however, be elastically preloaded in an axial direction, for example by means of disc springs ➤ Figure. The elastic preload ensures that the unloaded axial bearing component runs without slippage ➤ section. The preload also improves the operating behaviour of axial ball bearings and reduces running noise.
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Two needle roller/axial deep groove ball bearings NKX mounted in a mirror image arrangement and axially preloaded with disc springs
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Suitable for high axial loads
Needle roller/axial cylindrical roller bearings support high radial loads and also, due to the line contact of the cylindrical rollers, high axial loads in one direction ➤ Figure, ➤ Figure and ➤ Figure.
Mounting of two needle roller/axial cylindrical roller bearings in a mirror image arrangement
Needle roller/axial cylindrical roller bearings can support axial loads in one direction only. If no temperature-induced changes in length occur during operation in an arrangement of short shafts, two bearings can also be used to support axial loads in both directions, which are then mounted in a mirror image arrangement. The bearing parts should, however, be elastically preloaded in an axial direction, for example by means of disc springs ➤ Figure. The elastic preload ensures that the unloaded axial bearing component runs without slippage. The preload also improves the operating behaviour of needle roller/axial cylindrical roller bearings and reduces running noise.
NKIA for axial forces in one direction, NKIB for alternating axial forces
The radial bearing supports high radial forces, the angular contact ball bearing supports smaller axial forces. NKIA can support axial loads from one direction only ➤ Figure. NKIB has one narrow and one wide inner ring ➤ Figure. At the point where the inner rings join, there is a shoulder on both sides for guidance of the ball and cage assembly. As a result, these bearings are also suitable for supporting axial forces alternating in direction, i. e. as locating bearings, they can guide the shaft axially in both directions. The shaft is guided axially with an axial clearance of 0,08 mm to 0,25 mm.
In standard bearings of series NKIA and NKIB, the inner rings are matched to the enveloping circle tolerance F6 and can be interchanged with each other (mixed use) within the same accuracy class.
When mounting bearings NKIB, both inner ring parts must be located axially clearance-free against each other. The narrow inner ring has a larger bore diameter. This results in an interference fit if a shaft tolerance k6 is used.
Mounting of two needle roller/angular contact ball bearings in a mirror image arrangement
Needle roller/angular contact ball bearings NKIA support axial loads in one direction. In order to support axial loads in both directions, two bearings NKIA can also be used, which are then mounted in a mirror image arrangement ➤ Figure.
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Two needle roller/angular contact ball bearings NKIA mounted in a mirror image arrangement
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Preloading of the axial bearing component
The axial bearing component must be preloaded to 1% of the axial basic static load rating C0a (for example using disc springs). The basic load ratings C0a are stated in the product tables.
Shortening of the retaining rings where there is little distance between the shafts
In order to support axial forces, the bearings must be abutted by means of snap rings on the outer ring or a housing shoulder. If there is little distance between the shaft centres, the snap rings should be shortened ➤ Figure. Snap rings WR and SW are available from trade outlets. If the bearings are to support axial forces from alternating directions, two bearings must be fitted opposed to each other. The unloaded bearing must be axially preloaded, for example by means of disc springs ➤ Figure. This allows compensation of thermal expansion.
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Bearing arrangement with shortened snap rings
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If the surface of the shaft raceway is produced to DIN 617, the basic load ratings Cr in the product tables must be reduced by 15%.
The bearings are not suitable for the compensation of shaft misalignments relative to the housing
Combined needle roller bearings are not suitable for the compensation of angular misalignments. The extent to which a misalignment of the shaft can be tolerated relative to the housing bore is dependent on factors such as the design of the bearing arrangement, the size of the bearing, the operating clearance and the load etc. As a result, no guide value can be specified here for a possible misalignment. If angular misalignments occur, aligning needle roller bearings can, for example, be used in combination with an axial bearing, depending on the application.
In all cases, misalignments cause increased running noise, place increased strain on the cages and have a harmful influence on the operating life of the bearings.
Greasing of the radial bearing component prior to initial operation
In bearings with grease lubrication, the radial bearing component should be greased before initial operation using a grease of similar quality to that used in the axial bearing component.
Determining the relubrication interval
In order to determine the relubrication interval, values must be calculated separately for the axial and radial bearing components and the lower value should be used.
Compatibility with plastic cages
When using bearings with plastic cages, compatibility between the lubricant and the cage material must be ensured if synthetic oils, lubricating greases with a synthetic oil base or lubricants containing a high proportion of EP additives are used.
NX, NKX for oil lubrication, NX..-Z, NKX..-Z for grease lubrication
NX and NKX are intended for oil lubrication, therefore the bearings are not greased. Oil lubrication is carried out via the lubrication holes in the end cap ➤ Figure. If grease lubrication is intended, bearings of type NX..-Z or NXK..-Z should be used. In the case of these bearings, the axial bearing component is greased using a lithium complex soap grease to GA08. The end caps do not have lubrication holes.
Type NKX
Type NKX does not have a cap which holds the axial bearing component together ➤ Figure. As a result, these bearings are not self-retaining. They should be used with oil lubrication in preference, as the lubricating grease can only be retained with difficulty in the axial bearing component.
Type NKX..-Z
The bearings have an end cap without lubrication holes and are intended for grease lubrication ➤ section and ➤ Figure. The axial bearing component is greased using a lithium complex soap grease to GA08.
Type NKXR
As the bearings do not have an end cap, the lubricating grease can only be retained with difficulty in the axial bearing component ➤ Figure. They should therefore be lubricated using oil in preference.
Type NKXR..-Z
Bearings of this type have an end cap without lubrication holes and are intended for grease lubrication ➤ Figure. The axial bearing component is greased using a lithium complex soap grease to GA08.
Type NKIA, NKIB
Needle roller/angular contact ball bearings can be lubricated with oil or grease. For lubrication, the outer ring has a lubrication groove and a lubrication hole ➤ Figure and ➤ Figure. If grease lubrication is used, the radial and axial bearing components must be lubricated with the same grease prior to mounting the bearings.
Provide seals in the adjacent construction
Combined needle roller bearings are not sealed. In the case of unsealed bearings, sealing of the bearing position must be carried out in the adjacent construction. This must reliably prevent:
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Sealing of the bearing position in the adjacent construction – example
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End caps without lubrication holes are suitable for grease lubrication
Bearings of design Z have an end cap, which grips the axial bearing component ➤ section and ➤ Figure, ➤ Figure and ➤ Figure. End caps without lubrication holes form a gap seal and retain the lubricating grease in the axial bearing component (applies to types NX..-Z, NKX..‑Z, NKXR..-Z).
Limiting speeds and speed ratings in the product tables
The product tables generally give two speeds for the bearings:
The limiting speed nG is the kinematically permissible speed of a bearing. Even under favourable mounting and operating conditions, this value should not be exceeded without prior consultation with Schaeffler ➤ link. The values in the product tables are valid for oil lubrication.
Values for grease lubrication
For grease lubrication, 60% of the value stated in the product tables is permissible in each case.
nϑr is used to calculate nϑ
The thermal speed rating nϑr is not an application-oriented speed limit, but is a calculated ancillary value for determining the thermally safe operating speed nϑ ➤ link.
The thermally safe operating speed nϑr for NKXR, NKXR..-Z, NKIA and NKIB is given in the product tables. The speed rating nϑr to DIN ISO 15312:2004 is not defined for bearings NXand NKX and therefore only the limiting speed nG is given.
In order to calculate the thermally safe operating speed nϑ, NKXR(..-Z) must be regarded as axial bearings and NKIA, NKIB as radial bearings.
The Schaeffler Noise Index (SGI) is not yet available for this bearing type ➤ link. The data for these bearing series will be introduced and updated in stages.
Limiting values
The operating temperature of the bearings is limited by:
Possible operating temperatures of combined needler roller bearings ➤ Table.
Permissible temperature ranges
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Operating temperature |
Combined needle roller bearings Full complement bearings, bearings with a sheet steel cage |
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–30 °C to +120 °C |
In the event of anticipated temperatures which lie outside the stated values, please contact Schaeffler.
Sheet steel or plastic cages are used as standard
The cages of radial bearings are made from sheet steel or plastic and are closed on both sides ➤ link. Bearings with a polyamide cage PA66 have the suffix TV. The cages for the axial bearing component are closed on both sides or open on one side. Sheet steel or glass fibre reinforced polyamide PA66 are used here as standard, depending on the bearing type.
For high continuous temperatures and applications with difficult operating conditions, bearings with sheet steel cages should be used. If there is any uncertainty regarding cage suitability, please consult Schaeffler.
The standard is CN
As standard, combined needler roller bearings with inner ring have the radial internal clearance CN (normal) ➤ Table. CN is not stated in the designation.
The values for radial internal clearance in bearings with an inner ring correspond to DIN 620-4:2004 (ISO 5753-1:2009) ➤ Table. These are valid for bearings which are free from load and measurement forces (without elastic deformation).
For delivery options of bearings with a radial internal clearance value other than CN (for example C2, C3, C4) please consult Schaeffler.
Radial internal clearance of combined needle roller bearings with inner ring
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Nominal bore diameter |
Radial internal clearance |
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d |
CN |
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mm |
μm |
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over |
incl. |
min. |
max. |
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‒ |
24 |
20 |
45 |
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24 |
30 |
20 |
45 |
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30 |
40 |
25 |
50 |
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40 |
50 |
30 |
60 |
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50 |
65 |
40 |
70 |
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65 |
80 |
40 |
75 |
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80 |
100 |
50 |
85 |
For bearings without an inner ring, the enveloping circle diameter Fw is used
In the case of bearings without inner ring, the enveloping circle dimension Fw is used instead of the radial internal clearance. The enveloping circle is the inner inscribed circle of the needle rollers in clearance-free contact with the outer raceway. Once the bearings are mounted, the enveloping circle Fw is in the tolerance class F6. The precondition for this is that the bore tolerances are observed for bearings without an inner ring ➤ section and ➤ Table. Deviations for the tolerance class F6 ➤ Table.
Deviations for the enveloping circle diameter
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Enveloping circle diameter Fw |
Tolerance class F6 Tolerance for enveloping circle diameter Fw |
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|---|---|---|---|
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mm |
upper deviation |
lower deviation |
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over |
incl. |
μm |
μm |
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3 |
6 |
+18 |
+10 |
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6 |
10 |
+22 |
+13 |
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10 |
18 |
+27 |
+16 |
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18 |
30 |
+33 |
+20 |
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30 |
50 |
+41 |
+25 |
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50 |
80 |
+49 |
+30 |
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80 |
120 |
+58 |
+36 |
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120 |
180 |
+68 |
+43 |
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180 |
250 |
+79 |
+50 |
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250 |
315 |
+88 |
+56 |
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315 |
400 |
+98 |
+62 |
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400 |
500 |
+108 |
+68 |
The main dimensions of combined needle roller bearings correspond to ISO 15:2017 (DIN 616:2000 and DIN 5429-1:2005). This excludes needle roller/axial deep groove ball bearings of the types NX and NX..-Z, which are not standardised.
The limiting dimensions for chamfer dimensions correspond to DIN 620‑6:2004. Overview and limiting values ➤ section. Nominal value of chamfer dimension ➤ link.
The dimensional, geometrical and running tolerances of the bearings correspond to tolerance class Normal:
This excludes:
For a description of the suffixes used in this chapter ➤ Table and medias interchange http://www.schaeffler.de/std/1B69.
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Suffix |
Description of suffix |
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TV |
Bearing with radial cage made from |
Standard |
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XL |
X-life bearing |
Standard |
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Z |
Bearing with end cap, axial bearing component greased with lithium complex soap grease to GA08 |
Standard |
Examples of composition of bearing designation
The designation of bearings follows a set model. Examples ➤ Figure to ➤ Figure. The composition of designations is subject in part to DIN 623-1 ➤ Figure.
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Needle roller/axial deep groove ball bearing without inner ring, for grease lubrication: |
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Needler roller/axial cylindrical roller bearing, with end cap, with recommended inner ring: |
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Needle roller/angular contact ball bearing, double direction, with standard inner ring: |
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Separate calculation of the rating life for radial and axial bearing components
In the case of combined needle roller bearings, the rating life of the radial bearing and axial bearing component must always be calculated separately ➤ Equation and ➤ Equation. The lower value then applies in each case to the bearing position.
P = Fr and Fa respectively under purely radial load and purely axial load of constant magnitude and direction
The basic rating life equation L = (C/P)p used in the dimensioning of bearings under dynamic load assumes a concentrically acting load of constant magnitude and direction. In the case of radial bearings, this is a purely radial load Fr, while in the case of axial bearings it is a purely axial load Fa. In order to calculate the fatigue rating life for combined needle roller bearings, the bearing load Fr or Fa (Pr = Fr or Pa = Fa) is therefore used in the rating life for P ➤ Equation and ➤ Equation.
The radial component of the combined needle roller bearing may only be subjected to radial load. For the calculation of Pr ➤ Equation.
Equivalent dynamic load
Legend
| Pr | N |
Equivalent dynamic bearing load for the radial bearing |
| Fr | N |
Radial load |
The axial bearing can only be subjected to axial load. For the calculation of Pa under a concentrically acting axial load ➤ Equation.
For needle roller/angular contact ball bearings, the axial load Fa must not exceed 0,25 · Fr.
Equivalent dynamic load
Legend
| Pa | N |
Equivalent dynamic bearing load for the axial bearing component |
| Fa | N |
Axial load |
The equivalent static bearing load must be calculated for both the radial bearing and the axial bearing component ➤ Equation and ➤ Equation.
Equivalent static load
Equivalent static load
Legend
| P0r | N |
Equivalent static bearing load for the radial bearing |
| F0r | N |
Largest radial load present (maximum load) |
| P0a | N |
Equivalent static bearing load for the axial bearing component |
| F0a | N |
Largest radial load present (maximum load) |
S0a for needle roller/ angular contact ball bearings
In addition to the basic rating life L (L10h), it is also always necessary to check the static load safety factor S0 ➤ Equation. The calculation must be carried out for both the radial bearing (S0r) and the axial bearing component (S0a). The axial static load safety factor S0a must be ＞ 1,5.
Static load safety factor
Legend
| S0r, S0a | - |
Static load safety factor |
| C0r, C0a | N |
Basic static load rating |
| P0r, P0a | N |
Equivalent static bearing load |
In order to prevent damage due to slippage, a minimum radial load of P ＞ C0r/60 is required
In order that no slippage occurs between the contact partners, the radial bearing component must be constantly subjected to a sufficiently high load. For continuous operation, experience shows that a minimum radial load of the order of P ＞ C0r/60 is necessary. In most cases, however, the radial load is already higher than the requisite minimum load due to the weight of the supported parts and the external forces.
If the minimum radial load is lower than indicated above, please consult Schaeffler.
The axial component of the bearing arrangement must be preloaded to 1% of the axial basic static load rating C0a. Basic load ratings C0a ➤ link.
Support bearing rings over their entire circumference and width
In order to allow full utilisation of the load carrying capacity of the bearings and thus also achieve the requisite rating life, the bearing rings must be rigidly and uniformly supported by means of contact surfaces over their entire circumference and over the entire width of the raceway. Support can be provided by means of a cylindrical seating surface. The seating and contact surfaces should not be interrupted by grooves, holes or other recesses. The accuracy of mating parts must meet specific requirements ➤ Table and ➤ Table.
For secure radial location, tight fits are necessary
In addition to supporting the rings adequately, the bearings must also be securely located in a radial direction, to prevent creep of the bearing rings on the mating parts (shaft and housing bore) under load. This is generally achieved by means of tight fits between the bearing rings and the mating parts. If the rings are not secured adequately or correctly, this can cause severe damage to the bearings and adjacent machine parts. Influencing factors, such as the conditions of rotation, magnitude of the load, internal clearance, temperature conditions, design of the mating parts, mounting and dismounting options etc., must be taken into consideration in the selection of fits.
The following information provided in Technical principles must be taken into consideration in the design of bearing arrangements:
The bearings must also be securely located in an axial direction
As a tight fit alone is not normally sufficient to also locate the bearing rings securely on the shaft and in the housing bore in an axial direction, this must usually be achieved by means of an additional axial location or retention method. The axial location of the bearing rings must be matched to the type of bearing arrangement. Shaft and housing shoulders, retaining rings etc., are fundamentally suitable ➤ Figure, ➤ Figure and ➤ Figure. For locating bearings and for bearings with a split inner ring (type NKIB), axial abutment of the bearing rings on both sides is particularly important.
Axial location by snap ring
With types NX and NX..-Z, the retaining ring is inserted in the bearing slot in the bearing outer ring ➤ Figure. Snap rings which are inserted in the slot are a particularly compact and cost-effective way of locating the bearings axially in the housing. Suitable snap rings ➤ link. The snap rings must be ordered in addition to the bearing.
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Combined needle roller bearing NX with a retaining ring located axially in the housing
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The axial location of these bearings in one direction can take place by means of the needle roller bearing with integrated housing locating washer.
Tolerance classes and surface designs for the shaft and the housing bore ➤ Table and ➤ Table.
Tolerance classes and surface design for the shaft – bearings with inner ring
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Series |
Shaft tolerance |
Roundness tolerance |
Parallelism tolerance |
|---|---|---|---|
|
max. |
max. |
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|
NKIA, NKIB |
k6 Ⓔ |
IT4/2 |
IT4 |
|
NX, NKX, NKXR |
k6 Ⓔ | IT4/2 | IT4 |
Tolerance classes and surface design for the housing bore
|
Series |
Bore tolerance |
Roundness tolerance |
Parallelism tolerance |
|---|---|---|---|
|
max. |
max. |
||
|
NKIA, NKIB |
M6 Ⓔ |
IT5/2 |
IT4 |
|
NX, NKX, NKXR |
K6 Ⓔ, M6 Ⓔ (for rigid bearing arrangements) |
IT5/2 | IT4 |
Numerical values for ISO standard tolerances (IT grades) to ISO 286-1:2010
|
IT grade |
Nominal dimension in mm |
|||||
|---|---|---|---|---|---|---|
|
over |
6 |
10 |
18 |
30 |
50 |
|
|
incl. |
10 |
18 |
30 |
50 |
80 |
|
|
Values in μm |
||||||
|
IT4 |
4 |
5 |
6 |
7 |
8 |
|
|
IT5 |
6 |
8 |
9 |
11 |
13 |
|
|
IT6 |
9 |
11 |
13 |
16 |
19 |
|
|
IT7 |
15 |
18 |
21 |
25 |
30 |
|
Ra must not be too high
The roughness of the bearing seats must be matched to the tolerance class of the bearings. The mean roughness value Ra must not be too high, in order to maintain the interference loss within limits. The shafts must be ground, while the bores must be precision turned. Guide values as a function of the IT grade of bearing seating surfaces ➤ Table.
Roughness values for cylindrical bearing seating surfaces – guide values
|
Nominal diameter d (D) |
Recommended mean roughness value Ramax |
||||
|---|---|---|---|---|---|
|
mm |
μm |
||||
|
Diameter tolerance (IT grade) |
|||||
|
over |
incl. |
IT7 |
IT6 |
IT5 |
IT4 |
|
‒ |
80 |
1,6 |
0,8 |
0,4 |
0,2 |
The contact surfaces for the rings must be of sufficient height
The mounting dimensions of the shaft and housing shoulders, spacer rings and retaining rings etc., must ensure that the contact surfaces for the bearing rings are of sufficient height. Proven mounting dimensions for the radii and diameters of abutment shoulders are given in the product tables ➤ link. These dimensions are limiting dimensions (maximum or minimum dimensions); the actual values should not be higher or lower than specified.
The transition from the bearing seat to the abutment shoulder must be designed with rounding to DIN 5418 or an undercut to DIN 509. The maximum chamfer dimensions for the inner rings in accordance with DIN 620-6 must be taken into consideration.
For NKX and NKXR, the axial bearing component must be free in the housing
In order to avoid double fits, the diameter of the contact surface for the housing locating washer in the adjacent construction must be at least +0,5 mm larger than dimension D1 and D2 of the bearing washer in bearings NKX and NKXR ➤ Figure. Values for diameters D1 and D2 ➤ link.
|
Free housing locating washer in the adjacent construction for NKX and NKXR D1 = dimension of housing locating washer without end cap D2 = dimension of housing locating washer with end cap |
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Produce the raceway as a rolling bearing raceway
Where needle roller bearings without an inner ring are used (so-called direct bearing arrangements), the rolling elements run directly on the shaft. In these bearings, the raceway for the rolling elements on the shaft must be produced as a rolling bearing raceway (hardened and ground). Tolerances and surface designs are shown in ➤ Table. The surface hardness of the raceway must be 670 HV to 840 HV, the hardening depth CHD or SHD must be sufficiently large. If the shaft cannot be produced as a raceway, the bearings can be combined with inner rings IR ➤ section and ➤ link.
Tolerance classes and surface design for the shaft (direct bearing arrangement) – without inner ring
|
Series |
Shaft tolerance |
Roundness tolerance |
Parallelism tolerance |
Recommended mean roughness value |
|---|---|---|---|---|
|
Ramax (Rzmax) |
||||
|
max. |
max. |
μm |
||
|
NX, NKX, NKXR |
k6 Ⓔ |
IT3 |
IT3 |
0,1 (0,4) |
If the surface of the shaft raceway is produced to DIN 617, the basic load ratings Cr in the product tables must be reduced by 15%.
Through hardening steels in accordance with ISO 683-17 (e. g. 100Cr6) are suitable as materials for rolling bearing raceways in direct bearing arrangements. These steels can also be surface layer hardened.
Case hardening steels must correspond to DIN EN ISO 683-17 (e. g. 17MnCr5, 18CrNiMo7-6) or EN 10084 (e. g. 16MnCr5).
For flame and induction hardening, steels in accordance with DIN EN ISO 683-17 (e. g. C56E2, 43CrMo4) or DIN 17212 (e. g. Cf53) should be used.
If the raceway fulfils the requirements for rolling bearing materials but the raceway hardness is less than 670 HV, the load on the bearing arrangement cannot be as high as the full load carrying capacity of the bearing. In order to determine the dynamic and static load carrying capacity of the bearing arrangement, the basic dynamic load rating C of the bearings must be multiplied by the reduction factor fH (dynamic hardness factor) and the basic static load rating C0r by the reduction factor fH0 (static hardness factor) ➤ Figure and ➤ Figure.
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Dynamic hardness factor at reduced hardness of raceways/rolling elements fH = dynamic hardness factor HV, HRC = surface hardness |
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Static hardness factor at reduced hardness of raceways/rolling elements fH0 = static hardness factor HV, HRC = surface hardness
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Approximation value for case hardening depth
An approximation value for determining the minimum hardness depth is given in ➤ Equation. The reference value for the load present is the equivalent stress in accordance with the distortion energy hypothesis (DEH) as a function of the rolling element diameter Dw and the magnitude of the load.
Case hardening depth
Legend
| CHD | mm |
Case hardening depth |
| Dw | mm |
Rolling element diameter |
The local hardness must always be above the local requisite hardness, which can be calculated from the equivalent stress.
In these surface hardening methods, the load and contact geometry must be taken into consideration when determining the requisite hardening depth.
For calculation of the surface hardening depth SHD ➤ Equation:
Surface hardening depth
Legend
| SHD | mm |
Surface hardening depth |
| Dw | mm |
Rolling element diameter |
| Rp0,2 | N/mm2 |
Yield point of base material |
The mounting and dismounting options for combined needle roller bearings, by thermal, hydraulic or mechanical methods, must be taken into consideration in the design of the bearing position.
As the bearings are not self-retaining, they are easy to mount
Combined needle roller bearings without an end cap are not self-retaining. As a result, the bearing parts can be mounted separately from each other ➤ section. This gives simplified mounting of the bearings, especially when the two bearing rings have a tight fit.
Rolling bearings must be handled with great care
Rolling bearings are well-proven precision machine elements for the design of economical and reliable bearing arrangements, which offer high operational security. In order that these products can function correctly and achieve the envisaged operating life without detrimental effect, they must be handled with care.
The Schaeffler Mounting Handbook MH 1 gives comprehensive information about the correct storage, mounting, dismounting and maintenance of rotary rolling bearings http://www.schaeffler.de/std/1B68. It also provides information which should be observed by the designer, in relation to the mounting, dismounting and maintenance of bearings, in the original design of the bearing position. This book is available from Schaeffler on request.
The further development of products may also result in technical changes to catalogue products
Of central interest to Schaeffler is the further development and optimisation of its products and the satisfaction of its customers. In order that you, as the customer, can keep yourself optimally informed about the progress that is being made here and with regard to the current technical status of the products, we publish any product changes which differ from the printed version in our electronic product catalogue.
We therefore reserve the right to make changes to the data and illustrations in this catalogue. This catalogue reflects the status at the time of printing. More recent publications released by us (as printed or digital media) will automatically precede this catalogue if they involve the same subject. Therefore, please always use our electronic product catalogue to check whether more up-to-date information or modification notices exist for your desired product.
In addition to the data in this chapter, the following chapters in Technical principles must also be observed in the design of bearing arrangements:
